Telephonic circuit and apparatus



(No Model.) 3 Sheets-Sheet 1.

J. N. OULBERTSON. TELEPHONIG CIRCUIT AND APPARATUS.

No. 419,646. Patented Jan.21, 1890.

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3 Sheets- Sheet 2.

(No Model.) J. N. GULBERTSON.

TELEPHONIG CIRCUIT AND APPARATUS. No. 419,645. Patented Jan.21,1890.

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(No Model.) A 8 Sheets-Sheet 3. ,J. N. OULBERTSON. TELEPHONIG CIRCUITAND APPARATUS. No. 419,645. Patented Ja1L2L1890 W'zlnesseo'.

UNITED STATES PATENT OFFICE.

JOHN N. OULBERTSON, OF BUFFALO, NElV YORK, ASSIGNOR TO THE AMERI- OANBELL TELEPHONE COMPANY, OF BOSTON, MASSACHUSETTS.

TELEPHONIC CIRCUIT AND APPARATUS.

. SPECIFICATION forming part of Letters Patent No. 419,645, datedJanuary 21, 1890.

Application filed May 29, 1889. Serial No. 312,506- (No model.)

To all whom it may concern.-

Be it known that 1, JOHN N. CULBERTSON,

residing at Bu lfalo, in the county of Erie and State of New York, haveinvented certain Improvements in Telephone Circuits and Apparatus, ofwhich the following is a specification.

This invention refers to the art of electrically transmitting speech,and comprises peculiar arrangements of eircui tsand apparatus, wherebycertain advantages in economical Construction and maintenance and alsoin operation may be attained.

Ordinary single-line or earth return telephone-circuits are (when ofconsiderable length and when they pass in close proximity to circuitscarrying other classes of currents) subject to inductive disturbance dueto the presence and operation of the said foreign circuits, and are,moreover, always subject to disturbances arising from earth-currents. Itis, however, now well known that a maximum degree of efficiency inoperation and immunity from disturbance is reached when thetelephone-circuits are each provided with a return as well as anoutgoing wire, both wires being substantially parallel to each other andas close together as possible, so as to be practically equidistant fromany adjacent disturbing circuit. Such an organization is technicallystyled a metallic circuit, and its advantages arise from the fact thatby its use disturbing currents due to induction are in a manner wellunderstood neutralized, and that in consequence of the absence ofearth-terminals earth-currents are prevented from traversing thecircuit. In consequence of these decided advantages, which are inherentin the use of parallel Wire metallic circuits, the employment of suchcircuits has of late largely increased, and especially so in the case oflong lines and lines where the question of expense can be disregarded.

By reason of the fact that it is somewhat difficult to arrange andoperate connecting apparatus for the interconnection of metallic andearth rcturn-circuits when both classes enter the same central station,and also in view of the fact already stated of the improved results ofthe operation of metallic circuits, it would be decidedly advantageousif it were practicable to provide metallic circuits for all or amajority of the telephonelines without regard to length. Since, however,the use of metallic circuits implies a materially increased cost ofconstruction and maintenance, it has not so far been found practicableto universally adopt their employm ent, though their advantages, asrecited above, have universally been acknowledged, because in relativelysmall towns the compensation paid for the use of telephones is rarelysufficiently large to make metallic circuit construction remunerative.In other words, the question of expense cannot be dis regarded. To meetthis condition of affairs it has heretofore been suggested that ametallic circuit common to several subscribers stations and terminatingwith both of its ends at the central station could profitably beadopted, and that the several sub-station's connected with a centralstation could be in that case divided among a smaller number of metalliccircuits, those assigned to each circuit being connected in series withone another thereon. In the employment of this plan, while it is truethat each subscriber would toa certain extent participate in thebenefits accruing from the metallic circuit, it is also true that theseveral subscribers connected with any line would be constantlydisturbing and interfering with each other, as was found to occur inpractice in the earlier years of telephonic communication, when it wascustomary to connect several sub-stations with each earthreturn-circuit. Not only so, but the call-bell magnets at the severalsub-stations on such a combination line being actually in circuit whileconversation is in progress impede the proper operation of the line byreason of their resistance and likewise of the counter electro-motiveforces developed in them. This expedient, therefore, While notimpracticable, is non-practical and impolit-ic.

The object of my invention is to enable each member or subscriber of atelephone system to participate in the improved transmission accruingfrom the utilization of metallic circuits by means which shall be suf-10o ficiently economical in cost for universal adopt-ion, to providethat the subscriber at any moment using the line shall be perfectlysecured from the interruptions of other subscribers, and that thetalking-circuit shall be maintained at its maximum e'l'ficiency by theelimination of unnecessary resistance and by the absence ofelectromagnetic retardation and counter electro-motive forces arisingfrom the passage of alternating currents through elect-ro-magnets.

In the drawings which illustrate and form a part of this specification,Figure 1 is a diagram showing a telephone-circuit embodying one mode ofcarrying out my invention. Fig.

2 is a diagram illustrating a modified arrangement of circuits. Fig. 3is a diagram indieating more fully the modification shown in Fig. 2, andparticularly illustrating the centra-l-o'ffice connections therefor.Fig. 4 is a detail'indicating the applicability of my invention to mixedsystems of metallic and earth return-circuits; and Fig. 5 shows itsadaptation to single or independent circuits with which a large numberof sub-stations may be connected, and in which no interruption can occurwhile any station is talking with any other station.

In Fig. 1, 0 represents a central telephonestation whereto any number ofsub-station lines may converge, and A, A and A are respectivelysub-stations located at different points upon any one of the said linesD. As will be seen, the said line D comprises two distinct wires 2 and3, which each extend from the central station to each and all of thesubstations. Athird wireetextends from that one of the sub-stationswhich is nearest to the central station, and, passing through all of thesub-stations, terminates at the earth at the most distant one.

In the present case one of the main wires 3 is functionless, and is openor disconnected from the circuit at the central and at all substations.Its business is to serve when the line is being actually used forconversation as one side of a metallic circuit. The other main wire 2,when the circuit is at rest, is connected at the central station bymeans of the contact-spring s of its firal spring-jack J with theinsulated contactserew p, from whence the normal circuit passes inwardlyby wire 5 to the call-receiving annunciator (Z, and thence by wire 6 toits central-station earth-terminal E. Tracing the same wire 2, stillassuming the circuit to be at rest, it is found to lead to the mostdistant station, into which it is led by wire 2, while it also branchesinto the intermediate stations by branch wires 2 and 2 At eachsub-station there may be the usual subscribers outfit, comprisingreceiving and transmitting telephones, together with callbell,call-sending generator, and automatic telephone supportingswitch, thelatter three appliances being inclosed in the bell-box. The bell-box, asshown, has four screw-terminals, numbered, respectively, 9, 10, 11, and12, at its upper end, and six, numbered 13, 14, 15,

16, 17, and 18, at its lower end, and these terminals are for thepurpose of making the requisite connections between the circuits withinthe bell-box and the main lines on the one hand and thetelephone-instruments and battery on the other hand. Resuming ourconsideration of the main wire 2, itv will be observed that the saidbranches 2, 2 and 2, entering the sub-stations A, A and A all connectwith the screw-terminals 10. At the first sub-station this terminalconnects within the bell-box with two wires 20 and 22, while at theothers it has but one-viz, the wire 20; but if we trace any of the saidwires 20 we shall find that their circuits are discontinuous as long asthe receiving-telephone remains upon its support. The normal circuit isclearly, therefore, to be followed over' the remaining route by wire 22,which crosses over to terminal 11. Following this by wire 23, thecircuit leads through the generator 9 and contact-springs "L and k,which are normally held together by the depression of the hookswitch S,although insulated therefrom, to wire 24, which leads from the spring tothe lowest hinge 1, thence by wire 25, bell-magnet 1), wire 26, upperhinge 1, and wire 27 to terminal 12. Here a connection is made with thethird main wire 4, which, continuing on to the more distant stations, isfinally grounded at the last. Meanwhile entering station A from A, itconnects by branch 4 with bell-box terminal 11, passes through thegenerator, contacts iand 7t, and bell, as before, and leaving byterminal 12. Leavinstation A by wire 4 it passes on to station A whichits branch 4 enters at terminal 11. The calling appliances and contacts2' and 7; are at this station also traversed, and the circuit, going onto terminal 12 at the last station, passes out by branch i and the thirdwire 4 furnishin the sub-station end of the calling-circuit, terminatesfinallyand permanently at the earth E. Thus when all telephones are inplace at the sub-stations calls may be transmitted between any of thesaid sub-stations and the central station-that is, when at the centralstation the plug P is not inserted in the spring-jack and the spring .9therefore rests on the insulated pin 1), any sub-station may operate itsgenerator and affect the centralstation annunciator at the centralstation, provided no other sub-station 011 the same circuit is using theline conversationally; and in like manner, if the telephones at thesubstations are all in place, the operator at the central station mayinsert the plug P, press the call-key K, and operate'the generator M,thus sending the call-signal to any desired station; but it is evidentthat if any substation be already using the line for conversation itwill be impossible for any other to interrupt by the attempt to send acallsignal, for the reason that the several call generators and bells atall stations are in the circuit of the third main wire 4, and that ifany station on either side of that desiring to tacts i and 7c separatedfrom call be already using the line the circuit of the said third mainwire or ground-extension 4 is automatically opened there at the c011-tacts v and k, and it is also evident that for the same reason thecentral station cannot interrupt conversations if it should attempt tosend call-signals, which, however, would rarely occur, since the centraloperator is usually informed by the position of plugs or by suitabletests of the condition of the line.

It remains to consider the state of the circuit when in use forconversation, and in this regard it will be noted that the circuit is inthe drawings represented as being ready for use, the receiving-telephoneT being at station A removed from its support and the con each other,the calling-circuit of the series being thus opened.

If we trace the circuit now from the jackspring 8 at the central stationover wire 2, we shall find that its branch 2 is at station A open, thatleading through the telephones, because the receiver is still in place,and the springs f and it therefore out of contact, and that leadingthrough the calling appliances, because, though closed at stations A andA it is open at station A at contacts 1' and 7t. Its branch 2 at stationA is open for like reasons but arriving at station A we find a differentstate of affairs. The line 2 enters the bell B there by wire 2 andconnects with terminal 10. From this point a wire 20 leads directly tothe transmitting-telephone t by Way of screw 18, and the circuitcontinues to the receiving-telephone T by way of wire 21, screw 17,contact-springs h and f, wire 28, and screw 14, the said telephone beingconnected by wires 29 and 30 to the screws 13 and 14. From the screw 13awire 19 leads directly to the screw 9 at the upper end of the bell-box,which connects by branch 3 with main return-wire 3, leading back to thecentral station, where it is united to the metal frame a of the springjack J. A double conductor-plug P, made in a manner well understood forthe interconnection of metallic circuits, can :now be inserted, asshown, and when another similar plug attached to the other end of theconnectingcord N is likewiseinserted in the jack of the line with whichcommunication is desired the connection is complete, and the spring .9makes contact with the extreme end of the plug, while the shank of thesaid plug, insulated from the said extreme end, makes c011- taet in likemanner with the frame of the jack, these representing, respectively, the

central-station end of the lines 2 and 3. What. i

has been described is equally the case, the telephone T being removedfrom its support at any of the sub-stations.

The screw-terminals 15 and 16 at the lower end of the bell-boxes are forthe attachment of the primary transmitter-oircuit and battery-wires. Thecentral-station call, sending and talking appliances, including themagneto-generator M, the clearing-out annuneiator m, the call-keys K andK the telephones T and 25', are all connected, as shown at O, in amanner well understood, and fully described in Letters Patent issued toCharles E. Scribner, May 15, 1886, No. 383,018. For this reason andbecause they form no part of my invention, and may, in fact, besuperseded by any other form andarrangement of apparatus adapted toperform like functions, I have not thought it necessary to describe themin detail; but it is obvious from what has been stated that eachsub-station is provided with call, sending, and receiving appliancesserially included in a normally-closed calling-circuit extending betweenthe central and sub-stations; that the telephones of all stations areincluded in normally-open branches in multiple are or parallelism withone another between the two main wires of a talk ing metallic circuit,and that the removal of the receiving-telephone at any of thesub-stations operates to automatically open the calling-circuit of all,and, furthermore, to close the talking metallic circuit through thetelephones at its own station only.

In Figs. 2 and 3 no difference in principle is illustrated. The onlydifferentiation is that the wire 4, which extends between the first andlast sub-stations, is, instead of being grounded at the last station,there connected with the return talking-wire 3. This involves no changein function so far as the metallic talking-circuit is concerned; but itobviates the necessity of maintaining 'a ground connection both at thefinal substation and at the central station.

A consideration of Fig. 2 will show that all of the sub-stationapparatus is connected as in Fig. 1, but that the third or calling-lineextension 4, entering station A at screw-terminal 11, after passingthrough the generator 9, contacts 1' and 7c, and bell Z), goes on toscrew 12, from whence, instead of being connected to earth, it leads bya wire 4 to a connection at screw 9 with the branch 3 of return-line 3.Thus the calling-circuit as Well as the talking-circuit is made metallicand uses both main wires 2 and 3 between the central station and thenearest sub-station, while it uses the third line 4 and a portion of thereturnline 3 for the remaining line-section-viz., that between the firstand last sub-stations. Thus, supposing that none of the sub-stations areusing the line, and that consequently all receiving-telephones are inplace, the centralstation operator can, by uniting his callingappliances with the two ends of the outgoing and return wires 2 and 3,send call-signals and signal any desired station. The calling-circuit inthat case is over line 2 to station A, thence by branch 2 toscrew-terminal 10, cross-wire y, and through the generator g, contactsz' and 7c, and hell atsaid station A, and over wire 4 to the next andall succeeding stations, traversing at each their respective bells andgenerators and their lower switch-controlled contacts e la until thelast station is reached, where circuit is made by wire 4 with IIO thereturn-line 3, which now forms a part of the calling-circuit from thispoint back to the central station. lhe line 2 from the point 2 atstation A outwardly has no part in the calling-circuit and can beignored,because, although it enters all stations, the several branchesare all open'at the switch-spring h of the upper pair of contacts aslong as the telephones are in place and the switch-bars therebydepressed, and the line 3 is perfectly adapted to act as a call-circuitreturn, be-

cause, though it enters each station and normally is provided at eachstation with an open or disconnect-ed terminalnamely, the otherswitch-spring f-these disc-onnections do not impair the continuity ofthe main wire being in multiplearc with each other. On the other hand,when the line is in use for conversation, as indicated by the removal ofthe receiver from the switch at station A Fig. 2, the calling-line isopened, as in the case of Fig. 1, between the contacts z' and 7c, and nostation can therefore interrupt another by sending or attempting to sendcalling-signals, the calling apparatus being included in the circuit ofthe short additional line 4.,which now is thrown out of use, and thecontacts f and h in the same statioiibeing by the movement of the switchunited, the main direct and return lines 2 and 3 are connected throughthe telephones at that station, thus completing the metallic circuit forconversation.

The sub stat-ion connections are more clearly indicated in Fig. 3,where, however, station A is represented as using the circuit, and inwhich the central-station arrangements of the circuit are also shown.The main line 2, entering the central station, connects with the spring3 of the spring-jack at a given section of the multiple switch-board. Itgoes on through the contact-spring p by wire to to the spring of J 2 atthe next section, and from thence by Wire y to the final spring-jack JFrom the contact-screw of this jack it goes on to the annunciator d, andfrom the other terminal of said annunciator a wire. 3 is led, whichbranches to and unites with the conducting-frames of all of the severalspringjacks. When a double plug P, forming the terminal of a doubleconductoncord, is thrust into such a jack, the spring 3 is lifted fromthe insulated pin 1) and the original circuit is broken, but a new oneis formed, the spring .9, constituting the end of wire 2, making contactwith the end of the plug, and the frame at of the jack forming theterminal of line 3 making contact with the metal shank of the plug. Sucha circuit can now be connected with any other like line by inserting theplug P on the other end of the cord B into a springjack representingsuch line. Other jacks J indicating the presence of such other lines areshown; but for clearness their circuits are not carried out.

The organization shown in Fig. 4, strictly speaking, is not a part of myinvention, but is,

together with its description, introduced for the purpose of pointingout that the construction forming the essence of my invention is adaptedalike for use in exchange systems composed entirely of metallic circuitsand in exchanges which are compositely made up of both metallic andearth return-circuits. The same letters of reference are mainly employedas in the foregoing figures. L is an earth return-circuit, and L ametallic circuit, each having spring-jacks J. Circuit L, entering thespring-jack J by its wire 2, is attached to the spring 5, which restsupon the insulated pin 19, and, it being assumed that this is the finalspring-jack, the pin 19 is in turn connected by wire w with the earth atE after passing its annunciator d, where the circuit terminates. CircuitL on the other hand, also enters its jack J by wire 2,w'hich in thiscase is insulated from the metallic frame at, and, passing to theinsulated screw p, leads by wire 10, after passing its annunciator, to aconnection with its frame-wire 3, this, as shown in full in Fig. '3,leading out to the sub stations and serving as the metallic return. Ineffecting the union of such an earth circuit and metallic circuit aplugand cord arrangement is used, as shown. The plug P on theearth-circuit side is of solid metal, and is connected by the cord Rwith the sleeve portion (1 of the second plug P adapted for connectionwith the metalliccircuit spring-jacks. This sleeve is, as indicated inall of the drawings, insulated from the central portion, whichelectrically is continuous with the end piece q. The said end piececonnects with the wire R leading to earth. Now, if this flexibleconductor be caused to unite the two circuits L and L by the insertionof its plugs into their respective jacks, the combined circuit will beas follows: Coming in on wire 2 of circuit L,'which is grounded at adistant sub-station, it passes by way of spring 8, which is raised fromits pin, to plug P, conductor'R, sleeve g of plug P frame 7% of the jackof line L wire 3 of line L out to the sub-stations of said line, andback over wire 2 to spring 3, point q of plug P and conductor R toearth.

Fig. 5 is a diagram disclosing one of the most valuable and usefulexemplifications of my invention-that is, there are many telephone-lineswhich are technically known as private or club lines. These may havetheir stations disposed irregularly; but it is often convenient toarrange them, as in the drawings, so that a number of stations A in onedistrict may be placed in communication with a similar group D inanother district. Heretofore, if this has been attempted either by meansof earth return or metallic circuits, the stations have necessarily beenarranged in series, and all connections have been subject tointerruption from the calling apparatus of intermediate stations, andthe efficiency of transmission has also been impaired by reason of thecounter electro-motive forces developed by the intermediateelectromagnets.

It will be seen that by constructing a metalhc circuit for the main lineand by adding the third wire or calling-extension at both en both ofthese disadvantages are avoided. lhlsfigure may be understood byeference to Figs. 1, 2, and 3 by noting that the metalhe circuit,instead of leading to a central station, leads to a second group ofsub-stations, and that both ends of the circuit are provided with thecharacteristic feature of the former figuresviz., thecalling-extensionso arranged with reference to the two main wires thatthe removal of the receivingtelephone from its support opens thecallingcircuit, so that no other station can send signals, and alsoautomatically closes the metallic talking-circuit.

It does not seem necessary to describe the details of the internalconnections of the bell boxes, as they are in all respects similar tothose already described. The main metallic circuit L has two wires 2 and3. Both enter all stations by branches which are normally discontinuous,but which, when the switch is operated by the removal of the telephone,unite with each other to form a metallic loop including the telephones.The wire 2 at the outermost station of each group is connectedpermanently with the calling-extension 4, which traverses the stationsof said group, passing through the bell, generator, and a pair ofnormally-closed contactsin each station, the said contacts being adaptedto be separated when the telephone is removed from the switch. Thiscalling-extension is either, as shown in the figure, grounded at theterminal stations, or may in lieu thereof,

as in Figs. 2 and 3, be connected with the wire 3, thus completing thenormally-open metallic talking-circuit. 7

Having thus described my invention in detail and with reference to thedrawings, I will state that it comprises a telephone and signalingcircuit in which the calling or signaling appliances are includedserially in a normally -closed metallic or earth return circuit when theline is at rest, whereby any station in the circuit is enabled to calldirectly any other station, and in which the telephones at the severalstations are included in normally-open multiple-arc branches extendingbetween the main outgoing and return wires, and means, as shown, forautomatically closing the said telephone branches and for opening thecalling-circuit, whereby a metallic talking-circuit can be constitutedfrom any station to any otherstation free from interruption and fromelectro-magnetic retardation. It also comprises metallic circuitsextending from a central station to and through a group of substationsand normally open at each of the said sub-stations, but adapted to beclosed at any of the sub-stations through the telephones thereof for thepurpose of establishing a metallic talking-circuit having no interposedelectromagnets, combined with a calling or signaling extension thereforincluding the calling appliances of all the stations in series, the saidextension being permanently connected with one wire of the main circuitand serving to normally close the said circuit through the saidsignaling devices to earth or to the other wire of said main circuit, asdescribed.

It will be obvious that by the operation of my invention a number ofstations can be economically and efficiently operated upon the samemetallic circuit, and that any station using the line has a metalliccircuit to itself and is secure from interruption, its telephonecircuitbeing, moreover, absolutely free from elcctro-magnets. Since a branchline from each of the main lines 2 and3 runs into each sub-station, andsince these are when at work united through the telephones, it isevident that we may regard the two lines at each station as a loop.

I claim 1. A multiple-station metallic telephone and signaling circuitcomprising two main leads or wires extending from a central station tothe several sub-stations, provided at each sub-station with telephonesincluded in a normally-open multiple-arc branch, adapted, when closed,to unite the said main leads and to form a metallic circuit includingthe said telephones, and a normallyplosed signaling extension-conductorconnected with one of the said main wires at the sub-station nearest tothe central station, extending therefrom serially through the signalsendingand receiving appliances of all the sub-stations to the mostdistant sub-station, and being there united with a return-conductor,whereby Wh en the line is at rest a calling-circuit with the callingapparatus of the several stations in series is constituted, thetelephones being disconnected, and whereby when 'the said line is in usefor conversation a metallic circuit through the telephones of anydesired station may be constituted, the signaling-extension beingdisconnected.

2. A multiple-station metallic telephone and signal circuit comprising,substantially as hereinbefore described, two main leads or wiresextending from a central station to the several sub-stations, anormally-open branch circuit at each sub-station including telephones,the branches at the several sub-stations being in multiple arc with eachother, a normally-closed signaling-extension wire connecting permanentlywith one of the said main leads at the sub-station nearest to thecentral station and extending therefrom to a permanent connection withthe return-conductor at the most distant sub-station, signal sending andreceiving appliances at each substation, all connected in series in thecircuit of said signaling-exten sion, and circuit-changing devices ateach substation actuated automatically by the removal from its supportof the receiving-telephone at a given station to close the telephonebranch there, and thus constitute a metallic talking-circuit, and toopen the signaling-circuit and to restore the normal conditions by thereplacement of said telephone.

3. The combination, substantially as hereinbefore described, of acentral telephonest-ation, a series of sub-stations, a metallic circuitextendin g from the said central to the said sub stations, and providedat each with a norm ally-open loop-line, and telephones and acircuit-changer included therein, the several loops being in multiplearc with each other, a third or extension main wire permanently unitedwith one of the metallic-circuit main wires at the sub-station nearestto the central station and extending outward therefrom through all ofthe stations to a connection with the return -conductor at the laststation, signaling apparatus and a circuitchanger at each sub-station,all included serially in the said extension-wire, which is normallyclosed, and devices actuated automatically by the removal andreplacement of the receiving-telephone at a given station from or in itssupport to open the said signalingcir'cuit and close the telephonemetallic circuit at said station, or vice versa, whereby a metalliccircuit may be used in common by a number of stations, each having aclear line, and each being secured from being interrupted by the others.

4:- The combination, substantially as hereinbefore described, of ametallic telephone and signaling circuit extending between a series oftelephone-stations and provided with signaling or calling appliances ateach of the said sub-stations, all in series with each other, the saidcircuit being normally closed when at rest through the said signalingdevices, whereby any station is enabled to directly "call any otherstation, telephones at the several stations, each set being included ina normally-open multiple-arc branch extending between the two wires ofthe main circuit, and means, substantially as indicated herein,

' for automatically closing at any station the said telephone branchesand for opening the circuit through the signaling apparatus, whereby ametallic talking-circuit free from intermediate electro magnets isconstituted, and whereby it is made impossible for other stations on thesame circuit to interrupt con' versation by the transmission ofcall-signals.

5. In a telephone-circuit, two main lines, each forming one side of ametallic circuit and bothextending from a central to a series of substations, a third or extension line normally closed, but capable ofbeing broken at each station through the operation of the automatictelephone-supporting switch, the said third line including serially inits circuit the calling appliances of all stations and being arranged tounite one of the said main lines at the first station with the othermain line.

at the last station, and a direct bridge or branch line at each station,each including the telephones of its own station and normally open, butadapted to be closed by the removal of the receiving-telephone, andthereupon to unite the two main wires together at the same station, thetelephones of the said station being introduced into the metallictalking-circuit thus formed, substantially as and for the purposesdescribed.

(3. In a telephone system, ametallic circuit extending from a centralstation to and through a group of sub-stations, the two wires thereofbeing when at rest disconnected from each other at each of the saidsub-stations, but adapted to be connected with each other through thestation-telephon es by the removal of the receiving-telephone from itsresting position for the purpose of establishing a metallictalking-circuit having no interposed electro-magnets, combined with acalling or signaling extension-wire by means of which the main circuitis closed when at rest through the calling appliances of all thestations in series, which extension is adapted to be simultaneouslybroken for the purpose of preventing interrupting signals duringconversation, also by the removal of the telephone from its support, thenormal conditions being reestablished by the replacement of saidtelephone.

7. The combination, in atelephone system, of a central station, aswitch-board with spring-j acks located thereat, each spring jack havinga movable spring-contact and a metallic frame-piece insulated therefrom,a metallic or two-wire circuit extending from the said central stationto a series of distant substations, one of the wires thereof beingunited to the said contact-spring and the other to said frame, anextension-line permanently connected at the sub-station nearest to thesaid central station with that one of the main lines which is at thecentral station united to said movable contact -spring and passingthrough the magnets of the calling appliances at each of thesub-stations successively to a permanent connection at the most distantsub-station with the main wire leading from the frame of thecentral-station spring-jack, a normally-open cross-wire at each station,including the telephones, adapted to be closed during conversation andwhen closed to unite the two main lines through the said telephones, andautomatically-operated devices to effect the said closure andsimultaneously to open the signaling-extension, substantially asdescribed, and for the purposes specified.

8. The combination of a series of telephonestations, a metallic ordouble-wire circuit connecting the said stations, telephones at eachstation, a bridge-wire or loop-line at each station in circuit with thesaid tele-- IIO each station, an extension main line including in itscircuit the signaling appliances of all of the stations serially andconnecting at one of its ends With one of the main lines and at itsother end With the other main line and normally closing the circuit ofsaid main lines through the said signaling appliances, and means, asindicated, whereby the use of the telephone at any station is adapted toautomatically close the metallic main-line circuit through thetelephones at such station and simultaneously open the signaling-circuitof all stations, substantially as described.

9. A metallic telephone-circuit connecting a plurality of sub-stations,having the telephones at the several stations connected in loops-one ateach station-of the tWo Wires of the metallic circuit, and having thesignalinginstrimients of the several stations all connected in series ina third Wire normally uniting the two main Wires, the saidtelephoneloops being all normally open or discon tinuseveral stationsbeing all in seriesin the said 35 circuit.

In testimony whereof I have signed my name to this specification, in thepresence of two subscribing Witnesses, this 25th day of May, 1889.

JOHN N. CULBERTSON.

\Vitnesses:

H. O. PALMER; H. O. ALDRICH.

